Hellfire Dust

Hellfire Dust is the highly-flammable by-product left behind when Ground Netherrack is passed through a Hopper containing a Soul Sand filter.
It is an incredibly unstable substance that reacts violently when excessive heat is applied.

Crafting

Next, if you're going to be making a substantial amount of it, mechanically power the hopper first. Elsewise, see the below warning in the Keep in Mind section. After that, place a single piece of Soul Sand into the hopper's filter slot. If you're going to make Soul Urns at the same time, now would be when you'd attach the Urn to the bottom of the hopper.

If you're just making hellfire dust without making soul urns at the same time, skip this step and move on to the next. With the urn attached below it, place 8 Ground Netherrack on the top portion of the Hopper at a time, replacing the Urn every 8 pieces and collect the Hellfire Dust that is produced.

Without an urn attached, or if you just need the Hellfire Dust, as long as the hopper is powered you can pour as much Ground Netherrack into the Hopper setup as you need without fears of it blowing up in your face. Store in a dry, safe place for later use.

Needed for

Keep in Mind

Dropping more than 7 into the top of an unpoweredHopper without replacing the Soul Sand will cause the Hopper to break, losing half of the materials, the corner piece, and the pressure plate. It will also spawn you a cuddly new friend. This has been changed as of version 2.96 of Better Than Wolves.

Cooking off Hellfire Dust in any stoked appliance would not be a good idea...